The primary goal of these studies is to determine the interactions among the elements of idiotype-anti-idiotype (antigen receptor-antireceptor) networks in the regulation of immune responses and to assess the interactions of different idiotypic networks specific for the same hapten. Two heterogeneous idiotype (id) families (called 5AF6 and 3C6) associated with the BALB/c antibody response against the p-azophenylarsonate (Ar) hapten have been characterized and were found to be unrelated to each other or to the major A strain id (CRIa). These two id families are co-expressed in virtually all BALB/c mice, representing approximately 30% (5AF6) and 15% (3C6) of their total serum anti-Ar response. The 5AF6 id family is also expressed in A/J, RIII, CE, SEA, DBA, and RF strain mice. Small amounts of 3C6 id family were also found in C58, RIII, SEA, and PL strain mice. The 5AF6 family consists of two subsets based on the presence or absence of idiotopes associated with a monoclonal anti-Ar (called 2.4); strain differences in 5AF6 subset expression were observed. Several idiotopes are shared between the 5AF6 family and the minor CRI (CRIm) found in A/J mice. Anti-id treatment suggested that the two 5AF6 subsets, as well as the 3C6 family, were independently regulated from each other. 5AF6 family expression was dependent on appropriate allotype-linked (Igh-Ca) VH and the appropriate VL. All tested mouse strains except C58 were capable of supplying 5AF6 family VL. A negative regulatory effect on 5AF6 and 3C6 id expression also appeared to be associated with C58 mice. Five monoclonal anti-id specific for the 5AF6 family have been prepared in BALB/c(3) C.B.-20(2). Their specificity and biological significance are currently being examined. (LB)